Rhizosphere soil Metagenome

Nitrogen (N) shortage often hinders the bioremediation of mining-generated tailings. For pioneer plants living in the tailings, biological N fixation (BNF) is a non-negligible source of N. However, the diazotrophs in the rhizosphere of pioneer plants are rarely investigated. Using microbial community analysis, 15N2 DNA-SIP, and cultural screening methods, we investigated the roles of diazotrophs in the rhizosphere of pioneer plant Miscanthus sinensis. 15N2 DNA-SIP identified Stenotrophomonas and Pseudomonas as putative diazotrophs, which are also characterized as keystone taxa in the rhizosphere of M. sinensis grown in the tailings. The metagenome-assembled genomes of Stenotrophomonas and Pseudomonas contained some genes involved in BNF, plant growth promotion, and metal(loid) resistance. Subsequent diazotroph isolation and re-inoculation experiments further confirmed the nitrogenase activity and plant growth-promoting ability of the two keystone taxa. As such, this is one of the first studies to validate the role of keystone taxa in the M. sinensis rhizosphere in BNF and plant growth promotion, and it demonstrates that the statistical keystone taxa can be used for further screening and linking to microbiome functioning. Our findings revealed that the specialized keystone taxa participate in BNF, which provides an excellent opportunity to apply these keystone taxa as microbial agents in tailings bioremediation.